@mortommy I noticed that you are trying to send this command via the Karaf console when you replied in another thread…
This command contains the escape character (\) that openhab uses in strings:
POWR0 \r
What exactly do you want to send? Have you tried this?
POWR0 \\r
To help further it would be helpful if you connect the Null Modem cable you mention you have out of openhab and into a terminal program. Then tell us what you are TRYING to send out and what you see incoming to your terminal program. Once we confirm what is being sent out we can then look at the cause of you getting no replies.
Also you did not mention if you have tried different character sets (name which ones you have tried) as described as a new feature in the serial binding in the other thread…